The present invention relates to the alkylation of a diphenylamine compound. Alkylated diphenylamines have utility as antioxidants in lubricants, rubber compositions and plastics.
The prior art has sought to improve the alkylation of diphenylamine. For example, U.S. Pat. No. 2,943,112 discloses the purification of the crude alkylate by subsequent, selective alkylation of unreacted diphenylamine with certain olefins. U.S. Pat. No. 5,214,211 discloses rare earth pillared clays as catalysts for the alkylation of diphenylamine compounds. Other attempts to enhance the production of desirable monoalkylated diphenylamine and reduce the amount of unreacted diphenylamine reactant and undesirable dialkylated diphenylamine product are reported in U.S. Pat. Nos. 5,750,787 and 6,315,925.
An ionic liquid consists of inorganic and/or organic cations and anions, and typically has a very low vapor pressure, a wide liquid temperature range, and is non-flammable. Ionic liquids can act as a catalyst and/or solvent, and have been studied for utility as solvents, electrolytes, in separations and in fluid applications such as lubricants. See Holbrey, “Industrial Applications of Ionic Liquids,” Chemistry Today 35 (June 2004); Parkinson, “Ionic Liquids Make an Environmental Splash,” 100 Chemical Engineering Progress 7 (September 2004); and Drake et al., “Structural Effects on the Physical Properties of Ionic Liquids,” Air Force Research Laboratory Report No. AFRL-PR-ED-VG-2003-12 (May 2003).
The use of ionic liquids in Friedel-Crafts alkylation has been discussed in Wilkes, “Friedel-Crafts Reactions in Chloroaluminate Molten Salts,” Molten Salt Chemistry: An Introduction and Selected Applications 405 (Mamantov and Marassi Eds. 1987) and Earle et al., “Organic Synthesis,” Ionic Liquids in Synthesis 174 (Wasserschied & Welton Eds. 2003). However, neither study is directed to an alkylation reaction of a phenyl ring of a diphenylamine compound.
An object of the invention is to provide a synthesis which permits alkylation of a phenyl ring of a diphenylamine compound.
A feature of the invention is the use of an ionic liquid as a solvent and catalyst for the alkylation reaction.
An advantage of the invention is that use of an ionic liquid typically permits convenient separation of the alkylated diphenylamine compound(s) from the reaction mixture.